Middle distillate hydrogen treating processes



United States Patent 4 Claims ABSTRACT OF THE DISCLOSURE A process forthe production of low nitrogen and sulfur middle distillates having pourpoints below 0 F. and 80 E, which comprises catalytically treating ahigh pour point middle distillate with low nitrogen and sulfur contentsin the presence of hydrogen and a catalyst comprising alumina and anoble metal or a noble metal compound with the catalyst beingessentially free of fluorine or aluminum fluoride, at temperatures of700-850 F., pressures of 2002,000 p.s.i.g., and space velocities of0.210. Platinum-on-alumina is the preferred catalyst. Hydrocrackingprecedes pour point reduction, and hydrofining may precedehydrocracking.

This invention relates to processes for producing low pour point oilsfrom high pour point hydrocarbon oils. More particularly, the inventionrelates to the production of low pour point middle distillate fractionssuch as diesel fuel.

Middle distillate fractions, as the term is used herein, comprise thosehydrocarbon oils boiling above the gasoline boiling range and at leastpartly above the kerosene boiling range, i.e. hydrocarbon distillateshaving end boiling points of from about 600 F. to about 800 F. with aninitial boiling point of at least about 300 F. Middle distillates havingend boiling points in the range 650- 750 F. are particularly useful asdiesel fuel provided they meet the other product requirements for suchfuels. One such requirement where the diesel fuel is to be usable undercold weather conditions is that it have a low pour point of below 0 F.,frequently specified as no greater than about F., -20 F., or even lower.The requirement of a low pour point tends to dictate the use of oilshaving relatively low end boiling points, but it would be substantiallymore desirable that the oil have a higher end boiling point and arelatively low API gravity, preferably not over 39 API. The supply ofstraight run middle distillates having such a low pour point is quitelimited. Dewaxing of high pour point fractions to obtain a suitable lowpour point is expensive and difficult to accomplish with the distillatefractions. Numerous processes have been devised or proposed forproducing larger amounts of low pour point middle distillates byhydrocracking processes applied to higher-boiling feedstocks. Low pourpoint middle distillate fractions are obtainable from such hydrocrackingprocesses in relatively low yields, however, and operation of thehydrocracking processes to obtain higher middle distillate yieldsresults in the production of oils having unsatisfactorily high pourpoints.

It has now been found how to lower the pour point of middle distillatefractions with minimal yield loss. By means of the process of thepresent invention larger amounts of low pour point middle distillate canbe produced from heavy oils. Also, by the process of the invention therecan be produced from high-boiling oils gasoline and low pour pointmiddle distillate in nearly any desired relative amounts.

In accordance with the invention a heavy oil boiling at least partlyabove the middle distillate range, i.e. at least partly above 800 F., iscontacted with hydrogen at hydrocracking reaction conditions in thepresence of a solid catalyst having hydrogenation and cracking activity,and a sulfur-and-nitrogen-free middle distillate fraction is separatedfrom the contacted oil. The middle distillate fraction is then contactedwith hydrogen in the presence of a reforming catalyst at isomerizationreaction conditions. The contacting with the reforming catalyst iseffective to lower the pour point of the middle distillate fraction withminimal yield loss. At appropriate reaction conditions the API gravityof the middle distillate fraction can also be lowered.

In one embodiment a hetero-organic compound contaminated heavy oilboiling at least partly above the middle distillate range is contactedwith hydrogen at hydrocracking conditions in the presence of ahydrofining catalyst, and the contacted oil is separated into fractionsincluding a purified middle distillate fraction and a purifiedhigher-boiling fraction. At least a portion of the purified middledistillate fraction is then contacted with the reforming catalyst toobtain the low pour point middle distillate product. All or a portion ofthe purified higherboiling fraction can be recycled into contact withthe hydrofining catalyst to form additional purified middle distillatefraction. Thus the hetero-organic compound contaminated oil can berecycle hydrocracked to extinction using the hydrofining catalyst toobtain middle distillate and lower-boiling fractions, all of whichmiddle distillate fraction can be converted in high yield to low pourpoint middle distillate suitable as cold weather diesel fuel.

In another embodiment the higher-boiling fraction separated from thecontacting of a hetero-organic compound contaminated heavy oil with ahydrofining catalyst is contacted with hydrogen in the presence of anacidic hydrocracking catalyst at hydrocracking reaction conditions toform gasoline and additional purified middle distillate fraction.Gasoline and low pour point middle distillate are then recovered as theprincipal liquid products of the process. When the middle distillateproduced in the contacting with the hydrofining catalyst is converted tolow pour point middle distillate by contacting with the reformingcatalyst, and only the higher-boiling fraction is contacted with theacidic hydrocracking catalyst, the additional purified middle distillatefraction produced by the acidic hydrocracking catalyst contacting mayhave sufficiently low pour point that it can be blended directly withthe product of the reforming catalyst treatment.

In another embodiment, a hetero-organic compound contaminated heavy oilboiling substantialy above the middle distillate range is contacted in afirst stage reaction zone with hydrogen in the presence of a hydrofiningcatalyst at hydrofining reaction conditions effective to substantiallyhydrogenate the hetero-organic compound contaminated heavy oil boilingsubstantially above the at least a high-boiling oil portion thereof, isthen contacted with an acidic hydrocracking catalyst at hydrocrackingreaction conditions to form products including gasoline and middledistillate which will be essentially free of sulfur and nitrogencompounds. As in conventional two-stage hydrocracking processes of theprior art, the oil effluent of the second stage is separated intofractions including gasoline, middle distillate, and a higherboilingfraction. The higher-boiling fraction is recycled into contact with theacidic hydrocracking catalyst to form additional gasoline and middledistillate. The initial boiling point of the recycled fractioncorresponds substantially to the end boiling point of the middledistillate fraction, and is referred to as the recycle cut point. In theprocess it is found that as the recycle cut point is raised in an effortto increase the yield of middle distillate fraction, the pour point ofthe middle distillate fraction becomes higher. In general, the middledistillate pour point is above 20 F. at a recycle cut point which isstill below 650 F. In accordance with this embodiment of the invention,the recycle cut point is maintained in the range 650750 R, and the highpour point middle distillate fraction recovered is passed to a pourpoint reducing zone wherein it is contacted with hydrogen in thepresence of a reforming catalyst at isomerization re action conditions,and there is recovered middle distillate having a low pour point of notin excess of 20 F.

The attached drawing illustrates diagrammatically flow schemes suitablefor carrying out the process of this invention, incorporating several ofthe above-mentioned alternate embodiments.

Referring to the drawing, a heavy oil feed such as a cracked or straightrun heavy gas oil contaminated with hetero-oragnic compounds of sulfurand nitrogen is shown as comprising a heavy oil feed in line 11. The oilfeed passes via line 12 to nitrogen and sulfur removal zone 13 whereinit is contacted with hydrogen, shown as added through line 14, in thepresence of a sulfactive hydrogenation catalyst having hydrogenation andat least moderate hydrocracking activity. Suitable hydrofining catalystscomprise the transition metals and compounds thereof such as the oxidesor sulfides, alone or associated with inorganic refractory oxidecarriers. Preferred catalysts comprise the metals of Group VIII andthose of Group VI, alone or in combination, such as combinations ofnickel with tungsten or molybdenum, as sulfides. Suitable carrierscomprise alumina, alone or in combination with silica, zirconia,titania, or magnesia, or various combinations thereof. Alumino-silicatesof the molecular sieve type may also be used to advantage as carriers.The reaction conditions in zone 13 are such as to effect substantialconversion of the hetero-oragnic compounds to the hydrogenated inorganicby-products, such as Nl-I and H 8. Tvhe hydrofining reaction conditionsinclude temperatures in the range 600850 F. and pressures of 1000-4000p.s.i.g., with hydrogen-rich gas throughputs of 1,00020,000 s.c.f./bbl.and space velocities of 0.2l LHSV. Where hydrocracking reactionconditions are employed in zone 13, these will include temperatures of700-850 F. and pressures of 1000-4000 p.s.i.g. At these conditions andin the presence of a hydrofining catalyst having at least moderatehydrocracking activity at least a portion of the heavy oil feed whichboils above the middle distillate range is converted to middledistillate boiling range materials. Also, organic sulfu r and nitrogencompounds are substantially eliminated by conversion to H28 and NH3.

The efiluent of zone 13 passes via line 15 to a recovery zone 15,wherein any light gases formed are separated and removed through line17, gasoline boiling range materials are withdrawn through line 18, anda middle distillate fraction is withdrawn through line 19, any remainingportion of the feed which still boils above the middle distillate endboiling point being withdrawn through line 20. At least a portion of themiddle distillate fraction in line 19 is passed via lines 22 and 23 topour point lowering zone 24, if the middle distillate fraction is nearlyfree of sulfur and nitrogen compounds. Specifically, the sulfur contentof the oil should not exceed 50 p.p.m. by weight, and if the nitrogencontent is below 10 ppm. by weight this sulfur limitation will usuallybe met. More desirably, the sulfur content is below 15 ppm.

In the pour point lowering zone 24 the middle distillate is contactedwith hydrogen, introduced through line 25, in the presence of a catalysteffective for reforming gasoline boiling range hydrocarbons, atisomerization reaction conditions of 700-850 F. and 4004000 p.s.i.g.,with hydrogen-rich gas throughputs of 1,000-20,000 s.c.f./bbl. and spacevelocities of 0.210 LHSV. When the middle distillate of line 23 isessentially free of nitrogen and sulfur compounds, the reformingcatalyst is effective in isomerizing paraflin constituents of the middledistillate to lower pour point isoparafiins with minimal conversion tolower boiling fractions. The pour point can be lowered by more than 30F. with less than 10 percent conversion to gasoline and lighterproducts. Suitable catalysts comprise noble metals intimately associatedwith refractory oxide carriers of low cracking activity, a particularlysuitable catalyst being platinum on alumina. While the platinum onalumina catalyst may be promoted with a small amount of halide, theintroduction of acidic hydrocracking propensities into the catalyst isto be avoided. Thus, silica-alumina cracking catalyst carriers are notas suitable because at the elevated temperature conditions used in zone24 there would be excessive conversion to gasoline. With aplatinum-alumina reforming catalyst, the principal reaction appears tobe isomerization. It will be noted that the temperature employed isgenerally lower than is normally used with the catalyst in reforminggasoline boiling range hydrocarbons. If pressures in the range 400900p.s.i.g. are employed, however, it is possible to aromatize a portion ofthe naphthenic compounds in the middle distillate whereby a lowergravity middle distillate product is obtained. Thus, on passing theeffluent of pour point lowering zone 24 through line 26 to recoveryfacilities 27, there is obtained only a small amount of light productswithdrawn through line 28 and a high yield of low pour point middledistillate withdrawn through line 29.

In one embodiment of the invention, as illustrated, the portion of theefiluent of zone 13 which boils above the middle distillate end boilingpoint, in line 20, is recycled to extinction through line 21, returningto zone 13 via line 12. In another embodiment, all or a portion of thishigher-boiling fraction in line 20 is passed via lines 31 and 32 toboiling point lowering zone 33 wherein it is contacted with hydrogenshown as added through line 34. In zone 33 there is provided an acidichydrocracking catalyst and hydrocracking reaction conditions effectiveto convert the high boiling oil to gasoline and additional middledistillate fraction. Suitable catalysts comprise the Group VIII metalsor compounds thereof intimately associated with refractory oxidecarriers having acidic prop erties, such as an active cracking catalyst.The Group VIII metal may be one of the iron group metals or compoundssuch as the sulfide, particularly cobalt or nickel sulfide, or it may bea noble metal of the platinum-palladium group, Cracking catalystsconsisting of or comprising alumino-v silicates of the molecular sievetype provide a very effective acidic carrier for these metals when freeof alkali; metal.

Hydrocracking reaction conditions usable in zone 33 include temperaturesof 400-900 F. and pressures of 1000-4000 p.s.i.g., with hydrogen-richgas throughputs of LOGO-20,000 s.c.f./bbl. and space velocities of 02-10LHSV. Lower temperatures of 400750 F. can be employed if thehigh-boiling oil in line 32 is essentially free of nitrogen and sulfurcompounds, i.e. less than ppm. nitrogen by weight. If the oil stillcontains a significant amount of hetero-organic compound contaminantssuch as organic nitrogen, or by-product NH higher temperatures of above650 F. are used in zone 33.

Theefiluent of zone 33 passes via line 35 to recovery facilities 36wherein it is separated into fractions comprising light gases in line37, gasoline boiling range materials in line 33, a middle distillatefraction in line 40 and a higher-boiling fraction in line 41.Optionally, a kerosene product fraction may be taken off through line39. Generally, the higher-boiling fraction in line 41 will be recycledback to zone 33 via line 32. If the high-boiling fraction of line 20 andthe other constituents of the oil in line 32 comprise only materialsboiling above the middle distillate end boiling point, and if thematerial in line 32 is essentially free of nitrogen compounds, themiddle distillate product of line 40 will have a low pour point suchthat it can be blended directly with the low pour point of the middledistillate product of line 29 by passing through line 43. If, however,the oil of line 32 contains nitrogen compounds on particular, orincludes materials boiling in the middle distillate range, the pourpoint of the middle distillate in line 40 will be higher than desired inthe ultimate product. The middle distillate will, however, beessentially free of sulfur and nitrogen. Accordingly, this middledistillate can be passed via line 42 and line 23 to the pour pointlowering zone 24.

Thus, the relative amounts of middle distillate and gasoline products inthe over-all process can be adjusted in a variety of manners. In oneapproach, all or a portion of the middle distillate fraction of line 19is combined with the bottoms fraction of line 20 by passing through line30. Instead of recycling the bottoms through line 21, the broad boilingrange oil is passed through lines 31 and 32 to boiling point loweringzone 33. The recycle cut point, i.e. the initial boiling point ofrecycled oil in line 41, is maintained in the range 650750 F., and theresulting high pour point middle distillate recovered in line 40 ispassed via lines 42 and 23 to pour point lowering zone 24. A minimalyield of middle distillate can be obtained by employing a relatively lowrecycle cut point. When even greater yield of middle distillate isdesired than can be obtained by using the maximum recycle cut point, agreater portion of middle distillate is taken from line 19 of recoveryzone 16 and passed through lines 22 and 23 to the pour point loweringzone 24. The maximum yield of middle distillate is obtained bymaximizing the amount which is withdrawn from the first stage throughline 19 and passed to the pour point lowering zone, because the boilingpoint lowering accomplished in zone 33 always results in the productionof substantially more gasoline per barrel of feed than is obtained innitrogen and sulfur removal zone 13.

Catalysts usable respectively in zones 13, 24, and 33 may be prepared bya variety of suitable methods described in detail in the art. Auniversally suitable method comprises impregnating a preformed inorganicoxide carrier with a solution of a hydrogenation-dehydrogenationpromoting metal compound followed by drying and calcining. For example,a low silica content alumina-silica carrier may be impregnated withsolutions of nickel nitrate or chloride and ammonium molybdate to form acatalyst suitable for use in zone 13; activated alumina may beimpregnated with platinum chloride to form a catalyst for zone 24; andan acidic silica-alumina cracking catalyst carrier may be impregnatedwith nickel nitrate or other salt to form a catalyst for zone 33. Othertechniques such as coprecipitation or cogellation of all or part of thecarrier with all or part of the promoting metal can be used. Whenalumino-silicate zeolites are employed as carriers, all or part of thepromoting metal may be based exchanged for alkali metal or alkalineearth metal cations in the molecular sieve either directly or afterfirst exchanging for other cations.

The contacting of oil with hydrogen in the presence of the catalysts inthe respective zones may be carried in a variety of methods includingpassing the oil and hydrogen concurrently upwards or downwards, orcountercurrently, through fixed beds of catalyst particles containedWithin pressure vessel reactors. Other techniques such as the use ofmoving beds of catalyst particles, fluidized beds of finely dividedcatalyst particles, and reactor systems wherein the catalyst particlesare suspended as a slurry in the oil may also be used. The mostpreferred technique from the standpoint of design convenience and easeof operation is to pass preheated oil and hydrogen downwards through oneor more fixed beds of catalyst particles within a high pressure reactor,cool the efiluent to condense at least a portion of the oil and separatehydrogen-rich gas for recycling from the oil, and then separate the oilportion into fractions which are recovered or further treated in theother zones.

It will be recognized that the recovery zones 16, 27, and 36 may eachcomprise one or more distillation columns for obtaining betterseparation between and among the respective fractions. Further, in someinstances zone 16 and zone 36 may be combined into a single unit orcomplex of units. For example, when the higher boiling material in theeffluent of zone 13 is to be further converted to middle distillate inzone 33, and the middle distillates produced in zones 13 and 33 are tobe further treated for pour point lowering in zone 24, the efiluents ofzone 13 and zone 33 may pass to a common distillation column forseparation of a gasoline boiling range fraction, a middle distillatefraction to be further treated, and a higher-boiling recycle fraction.

In the following examples concurrent downflow of oil and hydrogenthrough fixed catalyst beds was employed, with separate fractionation ofthe effluents of the respective zones and recycle of hydrogen-rich gasin each zone. The first example illustrates that high yields of middledistillate can be produced by hydrocracking heavier oils with ahydrofining catalyst, but the middle distillate pour point isunsatisfactorily high.

Example 1 A heavy straight-run Arabian gas oil boiling from about 700 F.to about 1030 F. was recycle hydrocracked to gasoline and middledistillate fractions by contacting with a nickel sulfide-tungstensulfide silica-magnesia sulfactive hydrogenation catalyst havingmoderate hydrocracking activity at 750 F., 2000 p.s.i.g., 1.0 LHSV, with5,000 s.c.f./bbl. of recycle hydrogen. A middle distillate fractionboiling from about 300 F. to about 700 F. was recovered in volumepercent yield. This middle distillate fraction contained less than 1ppm. nitrogen and less than 10 ppm. sulfur after washing to removeammonia and H S, but had a pour point of 0 F.

The following example illustrates the pour point lowering obtainable bytreating the purified middle distillate with a reforming catalyst atelevated pressure.

Example 2 The sulfur-and-nitrogen-free middle distillate of the aboveexample was contacted with 1.0 percent platinum on alumina catalyst at780 F., 1800 p.s.i.g., 1.0 LHSV, with 6,000 s.c.f. H /bbl. Ninety-threevolume percent of the liquid product from contacting theplatinum-alumina reforming catalyst still boiled from 350 F. to 640 F.,and had a pour point of -70 F. as compared to the 7 pour point of F.determined for the nitrogen-andsulfur-free middle distillate feed.

The next example shows that API gravity can also be lowered whilelowering the pour point of middle distillate, in accordance with theinvention.

Example 3 The sulfur-and-nitrogen-free middle distillate having a pourpoint of 0 F. prepared as in Example 1 was contacted with theplatinum-alumina catalyst at 780 F. and a pressure of only 550 p.s.i.g.at 1.0 LHSV. Ninety percent of the liquid product boiled from 350 F. to650 F. and had a pour point of 60 F. In this case the gravity of the lowpour point product was lower than that of the nitrogen-and-sulfur-freemiddle distillate feed, 38.8 API as compared to 41.3 API, and the oilcontained about 30 volume percent aromatics as compared to 10 volumepercent aromatics in the feed.

Inspections of the feed and products in the foregoing examples aresummarized in the following Table I. The low cloud points of theisomerized oils are particularly to be noted, as it is desirable thatthe cold weather diesel fuel have a cloud point of not in excess of 0 F.

Distillation, ASTM The next example illustrates that the hydrocrackingprocess itself is not capable of achieving the low pour pointsobtainable on contacting with the platinum-alumina reforming catalystsand, further, that the low pour point oil obtainable is obtained at alower yield.

Example 4 A heavy straight-run gas oil boiling from about 700 F.

' to 1030 F. was contacted with a nickel sulfide-molybdenumsulfide-alumina-silica sulfactive hydrogenation catalyst having moderatehydrocracking activity at 760 F. and 2270 p.s.i.g. on a once-throughbasis at 0.8 LHSV with 5,000 s.c.f. H /bbl. About 70 volume percent ofthe feed was converted to materials boiling below 700 F., includingabout 56 volume percent boiling between 300 and 700 F. The 300700 F.middle distillate fraction had a gravity of 35.9 API and a pour point of45 F.

The next example illustrates the concurrent production of gasoline andlow pour point middle distillate by hydrocracking a purifiedhigher-boiling fraction with an acidic catalyst.

Example 5 The unconverted 30 volume percent of the oil in the aboveExample 4, boiling entirely above 700 F., was contacted with a nickelsulfide on acidic silica-alumina hydrocracking catalyst at 570 F., 1200p.s.i.g., and 0.8 LHSV with extinction recycle of material in theefilueut boiling above 650 F. (recycle cut point). In this hydrocrackingoperation most of the oil was converted to gasoline and lower-boilingdistillates, only a 30 volume percent yield of 300-650 F. middledistillate being obtained. The middle distillate, however, has a verylow pour point of below 60 F. The over-all yield of low pour pointmiddle distillate obtainable from the combination of oncethroughhydrocracking-hydrofining as in Example 4, and then recyclehydrocracking the bottoms as in this Example 5, amounts to about 64volume percent of middle distillate having a pour point of about -50 F.

The following example illustrates the embodiment of the inventionwherein the middle distillate fraction is produced by two-stagehydrocracking, and shows the eifect of recycle cut point on middledistillate pour point recovered from distillation in a single still ofthe efiluents of both stages.

Example 6 A straight-run heavy gas oil boiling from about 600 F. toabout 850 F. was contacted With a nickel sulfidemolybdenum sulfidealumina hydrofining catalyst at 700 F., 1430 p.s.i.g., and 0.5 LHSV on aonce-through basis to essentially eliminate organic sulfur and nitrogencontaminants. The sulfur-and-nitrogen-free liquid product was distilledto recover a middle distillate fraction boiling from 300 F. to therecycle cut point of the subsequent hydrocracking stage, and the bottomsfraction boiling above the recycle cut point was then contacted with anickel sulfide-silica-alumina acidic hydrocracking catalyst in a recycleoperation at about 520 F. and 1400 p.s.i.g. The efiluent from contactingthe acidic hydrocracking catalyst was combined with the first-stageefliuent for distillation into gasoline and lower-boiling fractions, themiddle distillate fraction, and the higher-boiling fraction which wasthe feed to the second stage. With a recycle cut point of 590 F. thereis obtained as the middle distillate fraction an oil boiling from 300 to590 F. with a pour point of about 49 F. in a yield of about 51 volumepercent. At a recycle cut point of 650 F., however, the middledistillate boils from about 300 F. to 650 F. and has a pour point of +2F. while the yield has increased to only 62 volume percent. At a recyclecut point of 630 F., the yield is 57 volume percent and the pour pointis 10 F.

It is to be noted that the middle distillate has a low pour point whenthe recycle cut point is below the feed initial boiling point. As thecut point is raised above the feed initial boiling point, the productpour point becomes higher due in part to the inclusion of unconvertedfeed in the product, as the feed boils partly within and partly abovethe middle distillate boiling range.

The next example illustrates the improvement of obtaining a greateryield of lower pour point middle distillate by adding a pour pointlowering stage and changing the operation of the two-stage process ofExample 6.

Example 7 In accordance with the invention, the recycle cut point in theacidic hydrocracking stage of Example 6 is maintained at 650 F. orabove, and the middle distillate fraction having a pour point of +2 F.or above is then contacted with the platinum-alumina reforming catalystat 750-800 F. and l5002000 p.s.i.g., whereby there is obtained middledistillate having a pour point well below 20 F. with minimal yield loss.

The yields and middle distillate pour points obtainable in the foregoingexamples are further summarized for comparison in the following TableII.

TABLE II Middle Distillate Produced Example Description Yield, vol.percent Pour Point, F.

1 Extinction recycle hydrocracking in 85 nitrogen and sulfur removalzone. 2 Pour point lowering of product of 93 (79% over-all). -70

Ex. 1 using reforming catalyst at 1,800 p.s.i.g. 3 Same as Ex. 2, at 550p.s.i.g 90 (76% over-all) -65 4. Once-through hydrocracking in 56 45nitrogen and sulfur removal zone. 5 Recycle hydrocracking 700+ F. 30 (9%over-all)--." --60 bottoms of Ex. 4 in boiling point lowering zone, 650F. BOP. 6 Two-stage recycle hydrocracking with single recovery still:

(a) 590 F. RC 51 -49 -38 5 10 +2 RC =recyelecut point.

As shown, the maximum yield of low pour point middle distillate isobtained by recycle hydrocracking a heavy oil in a single stage and thencontacting the middle distillate fraction produced, having a high pourpoint, with a reforming catalyst. Where a greater yield of gasoline ofhigher quality is desired concurrently with low pour point middledistillate, this can be accomplished by oncethrough hydrocracking in asulfur-and-nitrogen removal zone followed by once-through or recyclehydrocracking in a boiling point lowering zone with separation of amiddle distillate fraction either from both stages or only from thesecond stage. In either case, a high yield of lower pour point productis then obtainable by further treating the middle distillate with areforming catalyst in the pour point lowering zone.

It will be appreciated that a pour point as low as 60 F. is not alwaysneeded or even desired in diesel fuel or other middle distillateproducts. Operating conditions in the pour point lowering zone can beadjusted to obtain a desired pour point in the range between 0 F. and-80 F. An extremely low pour point product can be blended with otherhigher pour point oils. Also, the usual stabilizing additives, includingpour point depressants, can be incorporated into the finished product.

What is claimed is:

1. In a process for producing a middle distillate product boiling in therange of 300800 F., containing no more than 10 ppm. organic nitrogen and50 ppm. organic sulfur, and having a pour point between 0 F. and -80 F.,comprising catalytically treating a hydrocarbon fraction boiling withinsaid middle distillate range but having a pour point substantiallyhigher than said middle distillate in a pour point reducing zone in thepresence of hydrogen and a catalyst, at elevated temperatures andpressures, the improved method of operating said pour point reductionzone which comprises:

(a) using as said hydrocarbon fraction a fraction substantiallycomprising a portion of the eflluent of a previous hydrocracking stepwherein hydrocarbon feed boiling at least partly above 800 F. washydrocracked, said portion being further characterized by an organicnitrogen content of no more than 10 ppm. and an organic sulfur contentof no more than 50 p.-p.m.;

(b) reducing the pour point of said hydrocarbon fraction by at leastabout 60 F. by contacting said fraction in said pour point reducing zonewith hydrogen in the presence of a catalyst comprising alumina and anoble metal or noble metal compound, said catalyst being essentiallyfree of any halide, at pour point reduction conditions within the rangeof 700- 850 F., 4002,000 p.s.i.g., and 0.2-10 LHSV; and

(c) recovering from said zone a middle distillate product having anorganic nitrogen content of no more than 10 ppm, an organic sulfurcontent of no more than 50 p.p.m., and a pour point in the range of 0 F.to '80 F., said pour point being at least about 60 F. lower than thepour point of said hydrocarbon fraction used as the feed to said zone.

2. The process of claim 1, wherein said catalyst comprises platinum onalumina.

3. The process of claim 1, further characterized in that the feed tosaid hydrocracking step contains more than 10 ppm. organic nitrogen andmore than 50 p.p.m. organic sulfur, and said nitrogen and sulfurcontents are reduced in said hydrocracking step to less than 10 p.p.m.and less than 50 ppm, respectively, by catalytic hydrofiningaccomplished concurrently with catalytic hydrocracking.

4. The process of claim 1, further characterized in that ReferencesCited UNITED STATES PATENTS 3/1964 Tupman et al. 208-264 3/1965 Mason etal 208-60 DELBERT E. GANTZ, Primary Examiner.

A. RIMENS, Assistant Examiner.

US. Cl. X.R. 20860, 89

Patent No. 3,420,768 January 7, 1969 Ben G. Bray et al.

are in the above identified It is certified that error appe herebycorrected as patent and that said Letters Patent are shown below:

"contaminated heavy oil boiling substantially Column 3, line 7, cancelThe entire effluent from this above the and insert contaminants.

contacting, or

Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, IR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

